Coquina is the sedimentary rock formed by fragments or pieces of shells of marine animals like mollusks, brachiopods, trilobites and certain invertebrates.

The shells of marine animals are fragmented due to abrasion and mechanical degradation and sorting by the wave action and chemicals present in the sea water and gets transported which then sediments to form rock structures called coquina. The shells mostly contain calcium carbonate.

Chalk is the sedimentary rock formed b the fossil shells fragmented from foraminifers. This is a more powdery type of limestone.

Depending upon the type of sedimentation, sedimentary rocks are of three types:

Clastic – Made from sedimentation of clastic (pieces from broken rocks) through the processes of mechanical weathering and lithification (cementing and compacting). sandstone, conglomerate

Chemical – Made from evaporation of water and precipitation of materials which were previously dissolved in a solution. Example: Rock salt, dolomite

Organic – Repeated accumulation and sedimentation of organic matter or remains from plant and animal sources like bones (calcium deposits). Example: coal.

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